Imaging lens

ABSTRACT

An imaging lens includes a first lens group; a second lens group having positive refractive power; and a third lens group, arranged in this order from an object side to an image plane side. The first lens group includes a first lens having positive refractive power, a second lens, and a third lens. The second lens group includes a fourth lens and a fifth lens. The third lens group includes a sixth lens having negative refractive power and a seventh lens having negative refractive power. Each of the first lens and the second lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius. The seventh lens is formed in a shape so that a surface thereof on the object side has a negative curvature radius, and has a specific Abbe&#39;s number.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of a prior application Ser. No.15/260,399, filed on Sep. 9, 2016, pending, which claims priority ofJapanese Patent Application No. 2014-083530, filed on Apr. 15, 2014.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an imaging lens for forming an image ofan object on an imaging element such as a CCD sensor and a CMOS sensor.In particular, the present invention relates to an imaging lens suitablefor mounting in a relatively small camera such as a camera to be builtin a cellular phone, a portable information terminal, or the like, adigital still camera, a security camera, a vehicle onboard camera, and anetwork camera.

In these years, in place of cellular phones that are intended mainly formaking phone calls, so-called “smartphones”, i.e., multifunctionalcellular phones which can run various application software as well as avoice call function, have been more widely used. When applicationsoftware is run on smartphones, it is possible to perform functions suchas those of digital still cameras and car navigation systems on thesmartphones. In order to perform those various functions, most models ofsmartphones include cameras similar to the cellular phones.

Generally speaking, product groups of such smartphones are oftencomposed according to specifications for beginners to advanced users.Among them, an imaging lens to be mounted in a product designed for theadvanced users is required to have a high-resolution lens configurationso as to be also applicable to a high pixel count imaging element ofthese years.

As one of methods of attaining the high-resolution imaging lens, therehas been a method of increasing the number of lenses that compose theimaging lens. However, the increase of the number of lenses easilycauses an increase in the size of the imaging lens. Therefore, the lensconfiguration having a large number of lenses has a disadvantage interms of mounting in a small-sized camera such as the above-describedsmartphones. For this reason, conventional imaging lenses have beendeveloped so as to reduce the number of lenses therein as much aspossible. However, with rapid advancement in achieving the higher pixelcount of an imaging element in these days, an imaging lens has beendeveloped so as to attain higher resolution rather than a shorter totaltrack length of the imaging lens. For example, while it has beenconventionally common to mount a camera unit, which includes an imaginglens and an imaging element, inside a smartphone, in these years, therehas also been an attempt to attach a separate camera unit onto asmartphone, whereby it is possible to obtain images equivalent to thoseof digital still cameras.

In case of a lens configuration composed of seven lenses, due to thelarge number of lenses of the imaging lens, although it is slightlydisadvantageous for downsizing of the imaging lens, it has highflexibility in design. In addition, it has potential to attainsatisfactory correction of aberrations, and downsizing of the imaginglens in a balanced manner. For example, as the imaging lens having theseven-lens configuration as described above, an imaging lens describedin Patent Reference has been known.

Patent Reference: Japanese Patent Application Publication No.2012-155223

The conventional imaging lens described in Patent Reference includes afirst lens that has a shape of a biconvex shape, a second lens that hasa shape of a biconcave shape joined to the first lens, a third lens thatis negative and has a shape of a meniscus lens directing a convexsurface thereof to the object side, a fourth lens that is positive andhas a shape of a meniscus lens directing a concave surface thereof tothe object side, a fifth lens that is negative and directs a convexsurface thereof to the object side, a sixth lens that has a biconvexshape, and a seventh lens that has a biconcave shape, arranged in theorder from the object side. According to the conventional imaging lensof Patent Reference, the first through the fourth lenses compose a firstlens group and the fifth through the seventh lenses compose a secondlens group. With the configuration, it is designed to restrain a ratioof a focal length of the first lens group relative to that of the secondlens group within a certain range, so that it is achievable to downsizethe imaging lens and satisfactorily correct aberrations.

In case of the conventional imaging lens of Patent Reference, althoughthe size of the imaging lens is small, correction of the image surfaceis insufficient and the distortion is especially large. Therefore, thereis a limit by itself to achieve a high performance imaging lens. Withthe lens configuration of the imaging lens of Patent Reference, it isdifficult to achieve satisfactory aberration correction while downsizingof the imaging lens.

It should be noted that such a problem is not specific to the imaginglens to be mounted in cellular phones and smartphones. Rather, it is acommon problem for an imaging lens to be mounted in a relatively smallcamera such as digital still cameras, portable information terminals,security cameras, vehicle onboard cameras, and network cameras.

In view of the above-described problems of the conventional techniques,an object of the present invention is to provide an imaging lens thatcan attain both downsizing thereof and satisfactory aberrationcorrection.

Further objects and advantages of the present invention will be apparentfrom the following description of the invention.

SUMMARY OF THE INVENTION

In order to attain the objects described above, according to a firstaspect of the present invention, an imaging lens includes a first lensgroup having positive refractive power; a second lens group havingpositive refractive power, and a third lens group having negativerefractive power, arranged in the order from an object side to an imageplane side. The first lens group includes a first lens having positiverefractive power, a second lens having positive refractive power, and athird lens having negative refractive power. The second lens groupincludes a fourth lens and a fifth lens. The third lens group includes asixth lens having negative refractive power and a seventh lens havingnegative refractive power. According to the first aspect of theinvention, when the first lens has Abbe's number νd1, the second lenshas Abbe's number νd2, the third lens has Abbe's number νd3, the seventhlens has Abbe's number νd7, the first lens has a focal length f1, andthe second lens has a focal length f2, the imaging lens of the inventionsatisfies the following conditional expressions (1) through (5):40<νd1<75  (1)40<νd2<75  (2)20<νd3<35  (3)40<νd7<75  (4)2.5<f1/f2<30  (5)

According to the first aspect of the invention, the imaging lens of theinvention includes the first lens group having positive refractivepower, the second lens group having positive refractive power similarlyto the first lens group, and the third lens group having negativerefractive power, arranged in the order from the object side. Accordingto the first aspect of the invention, the arrangement of refractivepowers of the respective lens groups is “positive-positive-negative” inthe order from the object. Generally speaking, a chromatic aberration iscorrected by arranging the lens group having positive refractive powerand the lens group having negative refractive power in the order fromthe object side. In the lens configuration like this, in order todownsize the imaging lens, it is necessary to increase the refractivepower of the positive lens group, which is disposed on the object side.However, the refractive power of the lens group having positiverefractive power increases, it is often harder to satisfactorily correctthe chromatic aberration.

According to the first aspect of the invention, in the imaging lens, thepositive refractive power of the whole lens system is shared between thefirst lens group and the second lens group. For this reason, incomparison with when the number of lens groups having positiverefractive power is one, it is achievable to relatively keep weak therefractive powers of the positive lenses that compose the respectivelens groups. Therefore, according to the imaging lens of the invention,among the aberrations, especially the chromatic aberration issatisfactorily corrected, and thereby it is achievable to obtainsatisfactory image-forming performance, which is necessary forhigh-resolution imaging lens. In addition, according to the imaging lensof the invention, since the third lens group has negative refractivepower, it is achievable to suitably downsize the imaging lens.

The above-described first lens group is composed of three lenses, inwhich the arrangement of refractive powers thereof ispositive-positive-negative. Those three lenses are respectively formedfrom lens materials that satisfy the conditional expressions (1) through(3). The first lens, the second lens, and the third lens are acombination of low-dispersion materials and a high-dispersion material.With such arrangement of refractive powers of the respective lenses andthe arrangement of Abbe's numbers, in the first lens group, it issuitably restrain generation of chromatic aberration, and it issatisfactorily achieve correction of chromatic aberration, if anygenerated. Here, according to the imaging lens of the invention, thepositive refractive power is shared between two lenses, i.e., the firstlens and the second lens. Therefore, the respective refractive powers ofthe first lens and the second lens are kept relatively low. In addition,it is achievable to suitably downsize the imaging lens, whilesatisfactorily correcting the aberrations.

Moreover, as shown in the conditional expression (4), the seventh lens,which is disposed to be the closest to the image plane side in theimaging lens, is made of a low-dispersion material. Therefore, it isachievable to suitably restrain the chromatic aberration in the seventhlens, and in turn it is achievable to suitably restrain the chromaticaberration of the imaging lens.

When the imaging lens satisfies the conditional expression (5), it isachievable to suitably correct a coma aberration, astigmatism, and adistortion in a balanced manner, while downsizing the imaging lens. Whenthe value exceeds the upper limit of “30”, the refractive power of thesecond lens is strong relative to that of the first lens. Therefore, theback focal length is long, and it is easier to secure space to disposean insert such as an infrared cut-off filter. However, since the firstlens has relatively weak refractive power, it is disadvantageous fordownsizing of the imaging lens. In addition, an inner coma aberrationeasily occurs for off-axis light fluxes and a minus distortionincreases, so that it is difficult to obtain satisfactory image-formingperformance. On the other hand, when the value is below the lower limitof “2.5”, the first lens has strong refractive power relative to that ofthe second lens. Therefore, it is advantageous for downsizing of theimaging lens and satisfactory correction of the distortion. However, anouter coma aberration easily occurs for off-axis light fluxes and anastigmatic difference increases. Therefore, it is difficult to obtainsatisfactory image-forming performance.

According to a second aspect of the invention, when the whole lenssystem has a focal length f, and a composite focal length of the firstlens and the second lens is f12, the imaging lens having theabove-described configuration preferably satisfies the followingconditional expression (6):0.5<f12/f<1.1  (6)

When the imaging lens satisfies the conditional expression (6), it isachievable to restrain the chromatic aberration, the astigmatism, thedistortion, and the field curvature within preferred ranges. When thevalue exceeds the upper limit of “1.1”, the first lens group has weakpositive refractive power relative to the refractive power of the wholelens system. As a result, in the first lens group, the third lens hasrelatively strong negative refractive power. For this reason, in orderto satisfactorily correct the aberrations, it is necessary to weaken thenegative refractive power of the third lens. When third lens has weaknegative refractive power, the axial chromatic aberration isinsufficiently corrected (a focal position at a short wavelength movesto the object side relative to that at a reference wavelength) and thechromatic aberration of magnification for off-axis light fluxes atperiphery of the image is insufficiently corrected (an image-formingpoint at a short wavelength moves in a direction to be close to theoptical axis relative to that at a reference wavelength). Furthermore,since minus distortion increases, it is difficult to obtain satisfactoryimage-forming performance. On the other hand, when the value is belowthe lower limit of “0.5”, it is easy to correct the distortion and thechromatic aberration, but it is difficult to secure a back focal length.Moreover, the astigmatic difference increases at off-axis light fluxesat periphery of the image, so that it is difficult to obtainsatisfactory image-forming performance.

According to a third aspect of the invention, when the third lens has afocal length f3, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(7):−1.0<f2/f3<−0.2  (7)

When the imaging lens satisfies the conditional expression (7), it isachievable to satisfactorily correct the chromatic aberration, thedistortion, and the field curvature. When the value exceeds the upperlimit of “−0.2”, the third lens has weak negative refractive powerrelative to the positive refractive power of the second lens. Therefore,the axial chromatic aberration is insufficiently corrected and the minusdistortion increases. In addition, an image-forming surface curvestowards the object side, i.e., the field curvature is insufficientlycorrected. Therefore, it is difficult to obtain satisfactoryimage-forming performance. On the other hand, when the value is belowthe lower limit of “−1.0”, although it is advantageous for correctingthe distortion and the axial chromatic aberration, the image-formingsurface curves towards the image plane side, i.e., the field curvatureis excessively corrected. Therefore, also in this case, it is difficultto obtain satisfactory image-forming performance.

According to a fourth aspect of the invention, when the composite focallength of the first lens and the second lens is f12 and the third lenshas a focal length f3, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(8):−1.0<f12/f3<−0.1  (8)

When the imaging lens satisfies the conditional expression (8), it isachievable to restrain the off-axis coma aberration, the chromaticaberration, and the astigmatism respectively within preferred ranges inbalanced manner. When the value exceeds the upper limit of “−0.1”,although it is advantageous for downsizing of the imaging lens, theaxial chromatic aberration is insufficiently corrected and theastigmatic difference increases. In addition, an outer coma aberrationeasily occurs for the off-axis light fluxes, which is more difficult tocorrect. Therefore, it is difficult to obtain satisfactory image-formingperformance. On the other hand, when the value is below the lower limitof “−1.0”, it is advantageous for satisfactory correction of the axialchromatic aberration and for securing a back focal length. However,spherical aberration is insufficiently corrected and inner comaincreases, so that it is difficult to obtain satisfactory image-formingperformance.

According to a fifth aspect of the invention, when the whole lens systemhas a focal length f, and a composite focal length of the sixth lens andthe seventh lens is f67, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expression(9):−1.5<f67/f<−0.5  (9)

When the imaging lens satisfies the conditional expression (9), it isachievable to satisfactorily correct astigmatism, while downsizing theimaging lens. In addition, when the imaging lens satisfies theconditional expression (9), it is also achievable to restrain anincident angle of a light beam emitted from the imaging lens to theimage plane within the range of chief ray angle (CRA). As is well known,a so-called chief ray angle (CRA) is set in advance for an imagingelement, i.e. a range of an incident angle of a light beam that can betaken in the sensor, for an imaging element such as a CCD sensor or aCMOS sensor. Restraining the incident angle of a light beam emitted fromthe imaging lens to the image plane within the range of CRA, it isachievable to suitably restrain generation of shading, which is aphenomenon of obtaining a dark part on the periphery of the image.

When the value exceeds the upper limit of “−0.5” in the conditionalexpression (9), it is advantageous for downsizing the imaging lens.However, it is difficult to secure the back focal length. Moreover, inthe astigmatism, the sagittal image surface tilts to the object side andthe astigmatic difference increases. Therefore, it is difficult toobtain satisfactory image-forming performance. Moreover, it is difficultto restrain the incident angle of a light beam emitted from the imaginglens to the image plane within the range of CRA. On the other hand, whenthe value is below the lower limit of “−1.5”, it is advantageous forrestraining the incident angle within the range of CRA, but it isdifficult to downsize the imaging lens. Moreover, the chromaticaberration of magnification is insufficiently corrected at periphery ofthe image, and a minus distortion increases. Therefore, it is difficultto obtain satisfactory image-forming performance.

According to a sixth aspect of the invention, when the composite focallength of the fourth lens and the fifth lens is f45 and a compositefocal length of the sixth lens and the seventh lens is f67, the imaginglens having the above-described configuration preferably satisfies thefollowing conditional expression (10):−3<f45/f67<−0.8  (10)

When the imaging lens satisfies the conditional expression (10), it isachievable to satisfactorily correct a chromatic aberration ofmagnification, a distortion, and a field curvature, while restrainingthe incident angle of a light beam emitted from the imaging lens to theimage plane within the range of CRA. When the value exceeds the upperlimit of “−0.8”, it is easy to restrain the incident angle of a lightbeam emitted from the imaging lens to the image plane within the rangeof CRA. However, the minus distortion increases. Moreover, a chromaticaberration of magnification is insufficiently corrected at periphery ofthe image, and the field curvature is insufficiently corrected.Therefore, it is difficult to obtain satisfactory image-formingperformance. On the other hand, when the value is below the lower limitof “−3”, it is advantageous for correction of the chromatic aberrationof magnification and the distortion. However, the astigmatic differenceincreases, so that it is difficult to obtain satisfactory image-formingperformance.

According to a seventh aspect of the invention, when the sixth lens hasa focal length f6 and the seventh lens has a focal length f7, theimaging lens having the above-described configuration preferablysatisfies the following conditional expression (11):0.02<f7/f6<0.3  (11)

When the imaging lens satisfies the conditional expression (11), it isachievable to satisfactorily correct the distortion, the fieldcurvature, and the chromatic aberration of magnification, while securingthe back focal length. When the value exceeds the upper limit of upperlimit of “0.3”, it is advantageous for satisfactory correction of thechromatic aberration of magnification. However, it is difficult tosecure a back focal length. In addition, the field curvature isinsufficiently corrected and the minus distortion increases. Therefore,it is difficult to obtain satisfactory image-forming performance. On theother hand, when the value is below the lower limit of “0.02”, it iseasy to secure the back focal length. However, the chromatic aberrationof magnification increases at periphery of the image. Therefore, also inthis case, it is difficult to obtain satisfactory image-formingperformance.

According to an eighth aspect of the invention, when the whole lenssystem has a focal length f and a distance along the optical axisbetween the third lens and the fourth lens is D34, the imaging lenshaving the above-described configuration preferably satisfies thefollowing expression (12):0.03<D34/f<0.2  (12)

When the imaging lens satisfies the conditional expression (12), it isachievable to restrain the distortion, the astigmatism, and the fieldcurvature respectively within satisfactory ranges, while restraining theincident angle of a light beam emitted from the imaging lens to theimage plane within the range of CRA. When the value exceed the upperlimit of “0.2”, it is easy to restrain the incident angle of a lightbeam emitted from the imaging lens to the image plane within the rangeof CRA, and it is also easy to correct the distortion. However, it isdifficult to secure the back focal length. In addition, the fieldcurvature is excessively corrected and the astigmatic difference alsoincreases. Therefore, it is difficult to obtain satisfactoryimage-forming performance. On the other hand, when the value is belowthe lower limit of “0.03”, it is easy to secure the back focal length,but it is difficult to restrain the incident angle of a light beamemitted from the imaging lens to the image plane within the range ofCRA. Furthermore, since the minus distortion increases, it is difficultto obtain satisfactory image-forming performance.

According to the imaging lens of the present invention, it is possibleto provide a small-sized imaging lens that is especially suitable formounting in a small-sized camera, while having high resolution withsatisfactory correction of aberrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 1 according to an embodiment of thepresent invention;

FIG. 2 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 1;

FIG. 3 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 1;

FIG. 4 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 2 according to the embodiment of thepresent invention;

FIG. 5 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 4;

FIG. 6 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 4;

FIG. 7 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 3 according to the embodiment of thepresent invention;

FIG. 8 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 7;

FIG. 9 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 7;

FIG. 10 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 4 according to the embodiment ofthe present invention;

FIG. 11 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 10;

FIG. 12 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 10;

FIG. 13 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 5 according to the embodiment ofthe present invention;

FIG. 14 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 13;

FIG. 15 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 13.

FIG. 16 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 6 according to the embodiment ofthe present invention;

FIG. 17 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 16;

FIG. 18 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 16.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, referring to the accompanying drawings, an embodiment of thepresent invention will be fully described.

FIGS. 1, 4, 7, 10, 13, and 16 are schematic sectional views of theimaging lenses in Numerical Data Examples 1 to 6 according to theembodiment, respectively. Since the imaging lenses in those NumericalData Examples have the same basic configuration, the lens configurationof the embodiment will be described with reference to the illustrativesectional view of Numerical Data Example 1.

As shown in FIG. 1, according to the embodiment, the imaging lensincludes a first lens group G1 having positive refractive power, asecond lens group G2 having positive refractive power, and a third lensgroup G3 having negative refractive power, arranged in the order from anobject side to an image plane side. Between the third lens group G3 andan image plane IM of an imaging element, there is provided a filter 10.The filter 10 is omissible.

The first lens group G1 includes a first lens L1 having positiverefractive power, an aperture stop ST, a second lens L2 having positiverefractive power, and a third lens L3 having negative refractive power,arranged in the order from the object side. According to the imaginglens of the embodiment, the aperture stop ST is provided on an imageplane-side surface of the first lens L1. The position of the aperturestop ST is not limited to between the first lens L1 and the second lensL2 as in the imaging lens of Numerical Data Example 1. For example, theaperture stop ST may be disposed on the object side of the first lensL1. Accordingly, in case of a so-called “front aperture”-type lensconfiguration, in which the aperture stop ST is disposed on the objectside of the imaging lens, it is achievable to improve assemblingefficiency and to reduce the manufacturing cost of the imaging lens. Incase of the “aperture stop in front” type lens configuration, it is alsorelatively easy to shorten a total optical length of the imaging lens.Therefore, such lens configuration is an effective lens configurationfor mounting in portable devices, such as cellular phones andsmartphones that are widely used in these days. On the other hand, incase of a so-called “middle aperture”-type lens configuration, in whichthe aperture stop ST is disposed between the first lens L1 and thesecond lens L2 as in Numerical Data Example 1, an effective diameter ofthe first lens L1 is large in comparison with the total optical lengthof the imaging lens. As a result, the presence of the imaging lens in acamera is emphasized. Therefore, it is possible to appeal to users bythe luxurious impression, high lens performance, etc., as a part ofdesign of the camera.

In the first lens group G1, the first lens L1 is formed in a shape suchthat a curvature radius r1 of an object-side surface thereof and acurvature radius r2 of an image plane-side surface thereof are bothpositive, so as to have a shape of a meniscus lens directing a convexsurface thereof to an object side near an optical axis X. The shape ofthe first lens L1 is not limited to the one in Numerical Data Example 1.The first lens L1 can be formed in any shape, as long as the curvatureradius r1 of the object-side surface thereof is positive. Morespecifically, the first lens L1 can also be formed in a shape such thatthe curvature radius r2 is negative, so as to have a shape of a biconvexlens near the optical axis. Here, in order to more effectively attaindownsizing of the imaging lens, the first lens L1 is preferably formedto have a shape of a meniscus lens directing a convex surface thereof tothe object side near the optical axis X.

The second lens L2 is formed in a shape such that a curvature radius r3of an object-side surface thereof is positive and a curvature radius r4of an image plane-side surface thereof is negative, so as to have ashape of a biconvex lens near the optical axis X.

The third lens L3 is formed in a shape such that a curvature radius r5of an object-side surface thereof and a curvature radius r6 of an imageplane-side surface thereof are both positive, so as to have a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X. The shape of the third lens L3 is not limited to theone in Numerical Data Example 1. The third lens can be formed in anyshape, as long as the curvature radius r6 of the image plane-sidesurface is positive. Numerical Data Examples 2 through 4 are examples,in which the third lens L3 is formed in a shape, such that the curvatureradius r5 of the object side surface thereof is negative, i.e., so as tohave a shape of a biconcave lens near the optical axis X.

The second lens group G2 includes a fourth lens L4 having negativerefractive power, and a fifth lens L5 having positive refractive power,arranged in the order from the object side. The second lens group G2 canbe configured in any manner as long as the second lens group is composedof the two lenses and the composite refractive power of those two lensesis positive. Numerical Data Example 2 through 5 are examples, in whichthe second lens group G2 is composed of the fourth lens L4 havingpositive refractive power and the fifth lens L5 having negativerefractive power. Numerical Data Example 6 is an example, in which thesecond lens group G2 is composed of the fourth lens L4 and the fifthlens L5, which have positive refractive powers.

In the second lens group G2, the fourth lens L4 is formed in a shapesuch that a curvature radius r7 of an object-side surface thereof and acurvature radius r8 of an image plane-side surface thereof are bothnegative, so as to have a shape of a meniscus lens directing a concavesurface thereof to the object side near the optical axis X.

On the other hand, the fifth lens L5 is formed in a shape such that acurvature radius r9 of an object-side surface thereof is positive and acurvature radius r10 of an image plane-side surface thereof is negative,so as to have a shape of a biconvex lens near the optical axis X. Theshape of the fifth lens L5 is not limited to the one in Numerical DataExample 1. Numerical Data Examples 2 through 5 are examples, in whichthe fifth lens L5 is formed in a shape, such that the curvature radiusr10 is positive, i.e., so as to have a shape of a meniscus lensdirecting a convex surface thereof to the object side near the opticalaxis X. Numerical Data Example 6 is an example, in which the fifth lensL5 is formed in a shape, such that the curvature radius r9 is negative,i.e., so as to have a shape of a meniscus lens directing a concavesurface thereof to the object side near the optical axis X.

The third lens group G3 includes a sixth lens L6 having negativerefractive power, and a seventh lens L7 having negative refractivepower, arranged in the order from the object side. The sixth lens L6 isformed in a shape such that a curvature radius r11 of an object-sidesurface thereof and a curvature radius r12 of an image plane-sidesurface thereof are both positive, so as to have a shape of a meniscuslens directing a convex surface thereof to the object side near theoptical axis X.

The seventh lens L7 is formed in a shape such that a curvature radiusr13 of an object-side surface thereof is negative and a curvature radiusr14 of an image plane-side surface thereof is positive, so as to have ashape of a biconcave lens near the optical axis X. In the seventh lensL7, the object-side surface thereof and the image plane-side surfacethereof are formed as aspheric shapes, so as to have strong positiverefractive power as it goes to the periphery of the lens from theoptical axis X. With such shape of the seventh lens L7, it is achievableto satisfactorily correct off-axis chromatic aberration of magnificationas well as the axial chromatic aberration. In addition, it is alsoachievable to suitably restrain an incident angle of a light beamemitted from the imaging lens to the image plane IM within the range ofCRA.

The shape of the seventh lens L7 is not limited to the one in NumericalData Example 1. The seventh lens L7 can be formed in any shape, as longas the curvature radius r14 of the image plane-side surface thereof ispositive. Numerical Data Example 5 is an example, in which the seventhlens L7 is formed in a shape, such that the curvature radius r13 ispositive, so as to have a shape of a meniscus lens directing a convexsurface thereof to the object side near the optical axis X.

According to the embodiment, the imaging lens satisfies the followingconditional expressions (1) to (12):40<νd1<75  (1)40<νd2<75  (2)20<νd3<35  (3)40<νd7<75  (4)2.5<f1/f2<30  (5)0.5<f12/f<1.1  (6)−1.0<f2/f3<−0.2  (7)−1.0<f12/f3<−0.1  (8)−1.5<f67/f<−0.5  (9)−3<f45/f67<−0.8  (10)0.02<f7/f6<0.3  (11)0.03<D34/f<0.2  (12)νd1: Abbe's number of the first lens L1νd2: Abbe's number of the second lens L2νd3: Abbe's number of the third lens L3νd7: Abbe's number of the seventh lens L7f: Focal length of a whole lens systemf1: Focal length of the first lens L1f2: Focal length of the second lens L2f3: Focal length of the third lens L3f6: Focal length of the sixth lens L6f7: Focal length of the seventh lens L7f12: Composite focal length of the first lens L1 and the second lens L2f45: Composite focal length of the fourth lens L4 and the fifth lens L5f67: Composite focal length of the sixth lens L6 and the seventh lens L7D34: Distance on the optical axis X between the third lens L3 and thefourth lens L4

Here, it is not necessary to satisfy all of the conditional expressions,and it is achievable to obtain an effect corresponding to the respectiveconditional expression when any single one of the conditionalexpressions is individually satisfied.

In the embodiment, all lens surfaces are formed as an aspheric surface.When the aspheric shapes applied to the lens surfaces have an axis Z ina direction of the optical axis X, a height H in a directionperpendicular to the optical axis X, a conic constant k, and asphericcoefficients A₄, A₆, A₈, A₁₀, A₁₂, A₁₄, and A₁₆, the aspheric shapes ofthe lens surfaces are expressed with the following formula:

$Z = {\frac{\frac{H^{2}}{R}}{1 + \sqrt{1 - {\left( {k + 1} \right)\frac{H^{2}}{R^{2}}}}} + {A_{4}H^{4}} + {A_{6}H^{6}} + {A_{8}H^{8}} + {A_{10}H^{10}} + {A_{12}H^{12}} + {A_{14}H^{14}} + {A_{16}H^{16}}}$

Next, Numerical Data Examples of the imaging lens of the embodiment willbe described. In each Numerical Data Example, f represents a focallength of the whole lens system, Fno represents an F-number, and ωrepresents a half angle of view, respectively. In addition, i representsa surface number counted from the object side, r represents a curvatureradius, d represents a distance on the optical axis between lenssurfaces (surface spacing), nd represents a refractive index, and νdrepresents an Abbe's number, respectively. Here, aspheric surfaces areindicated with surface numbers i affixed with * (asterisk).

NUMERICAL DATA EXAMPLE 1

Basic data are shown below. f = 3.44 mm, Fno = 2.2, ω = 37.0° Unit: mmSurface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 2.255 0.3171.5346 56.1 (=νd1)  2* (Stop) 2.436 0.065  3* 2.400 0.500 1.5346 56.1(=νd2)  4* −8.336 0.071  5* 5.370 0.250 1.6355 24.0 (=νd3)  6* 2.9970.436 (=D34)  7* −1.358 0.315 1.5346 56.1 (=νd4)  8* −1.506 0.048  9*57.269 0.557 1.5346 56.1 (=νd5) 10* −1.579 0.072 11* 6.586 0.390 1.635524.0 (=νd6) 12* 5.835 0.197 13* −3.293 0.359 1.5346 56.1 (=νd7) 14*2.281 0.300 15 ∞ 0.200 1.5168 64.2 16 ∞ 0.601 (Image ∞ plane) AsphericSurface Data First Surface k = 0.000, A₄ = −1.114E−01, A₆ = 1.716E−01,A₈ = −6.753E−01, A₁₀ = 9.113E−01, A₁₂ = −4.349E−01, A₁₄ = −1.715E−01,A₁₆ = 2.030E−01 Second Surface k = 0.000, A₄ = −2.098E−01, A₆ =4.528E−01, A₈ = −3.217, A₁₀ = 6.995, A₁₂ = −4.687, A₁₄ = −2.463, A₁₆ =3.568 Third Surface k = 0.000, A₄ = −4.970E−02, A₆ = −1.500E−01, A₈ =−7.221E−01, A₁₀ = 1.724, A₁₂ = −6.829E−01, A₁₄ = −6.475E−01, A₁₆ =6.175E−01 Fourth Surface k = 0.000, A₄ = −2.271E−01, A₆ = −7.422E−02, A₈= 3.681E−02, A₁₀ = 4.386E−01, A₁₂ = −6.822E−01, A₁₄ = 3.633E−01, A₁₆ =1.075E−01 Fifth Surface k = 0.000, A₄ = −2.983E−01, A₆ = −5.158E−01, A₈= 1.744, A₁₀ = −2.258, A₁₂ = 1.053, A₁₄ = 8.637E−01, A₁₆ = −7.917E−01Sixth Surface k = 0.000, A₄ = −7.205E−02, A₆ = −4.150E−01, A₈ = 1.298,A₁₀ = −1.771, A₁₂ = 8.587E−01, A₁₄ = 2.137E−01, A₁₆ = −2.201E−01 SeventhSurface k = 0.000, A₄ = 2.681E−01, A₆ = −2.030E−01, A₈ = 2.977E−01, A₁₀= 5.153E−02, A₁₂ = −5.830E−01, A₁₄ = 3.652E−01, A₁₆ = −1.807E−02 EighthSurface k = 0.000, A₄ = 1.636E−01, A₆ = −1.044E−01, A₈ = 1.139E−01, A₁₀= −4.936E−02, A₁₂ = 4.089E−03, A₁₄ = −5.458E−03, A₁₆ = 7.198E−03 NinthSurface k = 0.000, A₄ = −2.036E−02, A₆ = 1.008E−01, A₈ = −9.426E−02, A₁₀= 3.535E−02, A₁₂ = 4.329E−03, A₁₄ = −6.757E−03, A₁₆ = 8.930E−04 TenthSurface k = 0.000, A₄ = 9.355E−02, A₆ = 6.215E−02, A₈ = 7.676E−03, A₁₀ =−9.918E−03, A₁₂ = −4.698E−04, A₁₄ = −2.538E−04, A₁₆ = 2.680E−04 EleventhSurface k = 0.000, A₄ = −9.058E−02, A₆ = 1.506E−02, A₈ = −7.881E−03, A₁₀= 7.829E−03, A₁₂ = −5.240E−04, A₁₄ = −3.709E−04, A₁₆ = −1.445E−04Twelfth Surface k = 0.000, A₄ = −1.402E−01, A₆ = 4.012E−02, A₈ =1.525E−03, A₁₀ = −2.457E−03, A₁₂ = −1.461E−05, A₁₄ = 1.635E−04, A₁₆ =−3.523E−05 Thirteenth Surface k = 0.000, A₄ = −6.802E−02, A₆ =1.037E−01, A₈ = −4.345E−02, A₁₀ = 1.099E−02, A₁₂ = −3.796E−03, A₁₄ =1.273E−03, A₁₆ = −1.683E−04 Fourteenth Surface k = 0.000, A₄ =−1.616E−01, A₆ = 1.157E−01, A₈ = −6.605E−02, A₁₀ = 2.465E−02, A₁₂ =−5.885E−03, A₁₄ = 8.025E−04, A₁₆ = −4.741E−05 f1 = 35.25 mm f2 = 3.54 mmf3 = −11.13 mm f4 = −99.63 mm f5 = 2.88 mm f6 = −100.83 mm f7 = −2.47 mmf12 = 3.38 mm f45 = 2.73 mm f67 = −2.45 mm

The values of the respective conditional expressions are as follows:f1/f2=9.95f12/f=0.98f2/f3=−0.32f12/f3=−0.30f67/f=−0.71f45/f67=−1.113f7/f6=0.024D34/f=0.13

Accordingly, the imaging lens of Numerical Data Example 1 satisfies theabove-described conditional expressions. The distance on the opticalaxis X from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 4.61 mm, anddownsizing of the imaging lens is attained.

FIG. 2 shows a lateral aberration that corresponds to a half angle ofview ω, which is divided into a tangential direction and a sagittaldirection (The same is true for FIGS. 5, 8, 11, 14, and 17).Furthermore, FIG. 3 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively. In the astigmatism diagram, anaberration on a sagittal image surface S and an aberration on atangential image surface T are respectively indicated (The same is truefor FIGS. 6, 9, 12, 15, and 18). As shown in FIGS. 2 and 3, according tothe imaging lens of Numerical Data Example 1, the aberrations aresatisfactorily corrected.

NUMERICAL DATA EXAMPLE 2

Basic data are shown below. f = 3.37 mm, Fno = 2.2, ω = 37.0° Unit: mmSurface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 1.687 0.3601.5346 56.1 (=νd1)  2* (Stop) 2.080 0.081  3* 2.069 0.627 1.5346 56.1(=νd2)  4* −2.335 0.012  5* −12.711 0.250 1.6355 24.0 (=νd3)  6* 2.9630.337 (=D34)  7* −1.851 0.511 1.5346 56.1 (=νd4)  8* −1.255 0.036  9*14.291 0.415 1.6355 24.0 (=νd5) 10* 11.555 0.060 11* 5.140 0.303 1.534656.1 (=νd6) 12* 3.728 0.151 13* −9.215 0.292 1.5346 56.1 (=νd7) 14*2.376 0.140 15 ∞ 0.200 1.5168 64.2 16 ∞ 0.501 (Image ∞ plane) AsphericSurface Data First Surface k = 0.000, A₄ = −1.035E−01, A₆ = 1.546E−01,A₈ = −6.963E−01, A₁₀ = 8.976E−01, A₁₂ = −4.726E−01, A₁₄ = −1.734E−01,A₁₆ = 2.316E−01 Second Surface k = 0.000, A₄ = −2.430E−01, A₆ =3.610E−01, A₈ = −3.129, A₁₀ = 7.060, A₁₂ = −4.768, A₁₄ = −2.712, A₁₆ =3.926 Third Surface k = 0.000, A₄ = −1.037E−01, A₆ = −2.199E−01, A₈ =−6.181E−01, A₁₀ = 1.739, A₁₂ = −6.029E−01, A₁₄ = −5.764E−01, A₁₆ =4.109E−01 Fourth Surface k = 0.000, A₄ = −1.993E−01, A₆ = 1.142E−02, A₈= 4.385E−02, A₁₀ = 5.225E−01, A₁₂ = −7.827E−01, A₁₄ = 1.273E−02, A₁₆ =4.693E−01 Fifth Surface k = 0.000, A₄ = −2.463E−01, A₆ = −5.153E−01, A₈= 1.901, A₁₀ = −2.250, A₁₂ = 7.890E−01, A₁₄ = 7.249E−01, A₁₆ =−4.881E−01 Sixth Surface k = 0.000, A₄ = −9.455E−03, A₆ = −4.924E−01, A₈= 1.270, A₁₀ = −1.695, A₁₂ = 8.868E−01, A₁₄ = 9.271E−02, A₁₆ =−1.255E−01 Seventh Surface k = 0.000, A₄ = 2.488E−01, A₆ = −9.798E−02,A₈ = 1.387E−01, A₁₀ = −5.087E−02, A₁₂ = −4.688E−01, A₁₄ = 4.874E−01, A₁₆= −1.679E−01 Eighth Surface k = 0.000, A₄ = 1.703E−01, A₆ = 6.899E−02,A₈ = 1.171E−01, A₁₀ = −6.243E−02, A₁₂ = −1.388E−02, A₁₄ = −3.738E−03,A₁₆ = 7.153E−03 Ninth Surface k = 0.000, A₄ = −1.639E−01, A₆ =1.073E−01, A₈ = −8.969E−02, A₁₀ = 9.542E−03, A₁₂ = −4.894E−03, A₁₄ =−4.582E−03, A₁₆ = 4.992E−03 Tenth Surface k = 0.000, A₄ = −1.500E−01, A₆= 5.422E−02, A₈ = −2.166E−02, A₁₀ = −9.624E−03, A₁₂ = 1.901E−03, A₁₄ =7.129E−04, A₁₆ = 6.232E−04 Eleventh Surface k = 0.000, A₄ = −2.030E−01,A₆ = 2.297E−03, A₈ = 2.201E−02, A₁₀ = 2.780E−04, A₁₂ = 6.385E−04, A₁₄ =−7.657E−05, A₁₆ = −2.699E−04 Twelfth Surface k = 0.000, A₄ = −1.577E−01,A₆ = 2.996E−02, A₈ = 2.442E−03, A₁₀ = −2.418E−03, A₁₂ = −2.139E−04, A₁₄= 1.344E−04, A₁₆ = 1.979E−05 Thirteenth Surface k = 0.000, A₄ =−9.538E−02, A₆ = 9.840E−02, A₈ = −4.715E−02, A₁₀ = 1.099E−02, A₁₂ =−3.581E−03, A₁₄ = 1.355E−03, A₁₆ = −1.798E−04 Fourteenth Surface k =0.000, A₄ = −2.024E−01, A₆ = 1.307E−01, A₈ = −6.820E−02, A₁₀ =2.474E−02, A₁₂ = −5.882E−03, A₁₄ = 7.922E−04, A₁₆ = −4.563E−05 f1 =12.65 mm f2 = 2.16 mm f3 = −3.76 mm f4 = 5.61 mm f5 = −100.94 mm f6 =−27.45 mm f7 = −3.50 mm f12 = 2.01 mm f45 = 5.88 mm f67 = −3.13 mm

The values of the respective conditional expressions are as follows:f1/f2=5.86f12/f=0.60f2/f3=−0.57f12/f3=−0.54f67/f=−0.93f45/f67=−1.88f7/f6=0.13D34/f=0.10

Accordingly, the imaging lens of Numerical Data Example 2 satisfies theabove-described conditional expressions. The distance on the opticalaxis from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 4.21 mm, anddownsizing of the imaging lens is attained.

FIG. 5 shows a lateral aberration that corresponds to the half angle ofview ω, and FIG. 6 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively, for the imaging lens of NumericalData Example 2. As shown in FIGS. 5 and 6, according to the imaging lensof Numerical Data Example 2, the aberrations are also satisfactorilycorrected.

NUMERICAL DATA EXAMPLE 3

Basic data are shown below. f = 3.37 mm, Fno = 2.3, ω = 37.0° Unit: mmSurface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 1.680 0.3861.5346 56.1 (=νd1)  2* (Stop) 2.599 0.104  3* 3.000 0.626 1.5346 56.1(=νd2)  4* −1.962 0.078  5* −3.345 0.250 1.6355 24.0 (=νd3)  6* 2.8820.238 (=D34)  7* −2.871 0.452 1.5346 56.1 (=νd4)  8* −1.267 0.050  9*11.980 0.486 1.6355 24.0 (=νd5) 10* 9.931 0.170 11* 4.056 0.300 1.534656.1 (=νd6) 12* 3.372 0.157 13* −23.911 0.310 1.5346 56.1 (=νd7) 14*2.380 0.200 15 ∞ 0.200 1.5168 64.2 16 ∞ 0.414 (Image ∞ plane) AsphericSurface Data First Surface k = 0.000, A₄ = −8.241E−02, A₆ = 1.518E−01,A₈ = −6.952E−01, A₁₀ = 8.909E−01, A₁₂ = −4.931E−01, A₁₄ = −1.811E−01,A₁₆ = 2.666E−01 Second Surface k = 0.000, A₄ = −2.275E−01, A₆ =3.836E−01, A₈ = −3.017, A₁₀ = 6.945, A₁₂ = −4.983, A₁₄ = −2.666, A₁₆ =4.176 Third Surface k = 0.000, A₄ = −1.432E−01, A₆ = −1.337E−01, A₈ =−6.040E−01, A₁₀ = 1.794, A₁₂ = −6.104E−01, A₁₄ = −7.571E−01, A₁₆ =2.584E−01 Fourth Surface k = 0.000, A₄ = −1.073E−01, A₆ = −5.463E−02, A₈= −4.255E−03, A₁₀ = 5.463E−01, A₁₂ = −6.893E−01, A₁₄ = −1.210E−02, A₁₆ =1.850E−01 Fifth Surface k = 0.000, A₄ = −2.576E−01, A₆ = −4.667E−01, A₈= 1.903, A₁₀ = −2.336, A₁₂ = 6.689E−01, A₁₄ = 7.776E−01, A₁₆ =−4.608E−01 Sixth Surface k = 0.000, A₄ = −7.944E−02, A₆ = −4.418E−01, A₈= 1.276, A₁₀ = −1.711, A₁₂ = 8.974E−01, A₁₄ = 6.691E−02, A₁₆ =−1.087E−01 Seventh Surface k = 0.000, A₄ = 2.513E−01, A₆ = −1.421E−01,A₈ = 1.263E−01, A₁₀ = −1.827E−02, A₁₂ = −4.186E−01, A₁₄ = 5.029E−01, A₁₆= −1.843E−01 Eighth Surface k = 0.000, A₄ = 1.919E−01, A₆ = 7.248E−02,A₈ = 1.153E−01, A₁₀ = −6.760E−02, A₁₂ = −2.090E−02, A₁₄ = −5.478E−03,A₁₆ = 9.951E−03 Ninth Surface k = 0.000, A₄ = −1.001E−01, A₆ =9.987E−02, A₈ = −9.297E−02, A₁₀ = 1.434E−02, A₁₂ = 1.058E−05, A₁₄ =−2.628E−03, A₁₆ = 2.872E−03 Tenth Surface k = 0.000, A₄ = −1.569E−01, A₆= 5.735E−02, A₈ = −1.942E−02, A₁₀ = −9.047E−03, A₁₂ = 1.646E−03, A₁₄ =4.727E−04, A₁₆ = 5.869E−04 Eleventh Surface k = 0.000, A₄ = −2.248E−01,A₆ = 1.366E−03, A₈ = 2.158E−02, A₁₀ = 1.515E−04, A₁₂ = 6.444E−04, A₁₄ =−3.185E−05, A₁₆ = −2.051E−04 Twelfth Surface k = 0.000, A₄ = −1.554E−01,A₆ = 2.774E−02, A₈ = 2.233E−03, A₁₀ = −2.424E−03, A₁₂ = −2.127E−04, A₁₄= 1.357E−04, A₁₆ = 1.991E−05 Thirteenth Surface k = 0.000, A₄ =−1.038E−01, A₆ = 9.883E−02, A₈ = −4.721E−02, A₁₀ = 1.096E−02, A₁₂ =−3.591E−03, A₁₄ = 1.353E−03, A₁₆ = −1.801E−04 Fourteenth Surface k =0.000, A₄ = −1.990E−01, A₆ = 1.305E−01, A₈ = −6.810E−02, A₁₀ =2.478E−02, A₁₂ = −5.877E−03, A₁₄ = 7.925E−04, A₁₆ = −4.580E−05 f1 = 7.75mm f2 = 2.32 mm f3 = −2.40 mm f4 = 3.86 mm f5 = −100.64 mm f6 = −44.16mm f7 = −4.03 mm f12 = 1.98 mm f45 = 3.95 mm f67 = −3.76 mm

The values of the respective conditional expressions are as follows:f1/f2=3.34f12/f=0.59f2/f3=−0.97f12/f3=−0.83f67/f=−1.11f45/f67=−1.05f7/f6=0.091D34/f=0.070

Accordingly, the imaging lens of Numerical Data Example 3 satisfies theabove-described conditional expressions. The distance on the opticalaxis from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 4.35 mm, anddownsizing of the imaging lens is attained.

FIG. 8 shows a lateral aberration that corresponds to the half angle ofview ω, and FIG. 9 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively, for the imaging lens of NumericalData Example 3. As shown in FIGS. 8 and 9, according to the imaging lensof Numerical Data Example 3, the aberrations are also satisfactorilycorrected.

NUMERICAL DATA EXAMPLE 4

Basic data are shown below. f = 3.37 mm, Fno = 2.2, ω = 37.0° Unit: mmSurface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 1.740 0.3531.5346 56.1 (=νd1)  2* (Stop) 2.078 0.074  3* 2.105 0.642 1.5346 56.1(=νd2)  4* −2.421 0.021  5* −17.903 0.250 1.6355 24.0 (=νd3)  6* 3.5400.331 (=D34)  7* −1.594 0.450 1.5346 56.1 (=νd4)  8* −1.251 0.058  9*11.093 0.445 1.6355 24.0 (=νd5) 10* 6.053 0.070 11* 4.217 0.319 1.534656.1 (=νd6) 12* 3.806 0.129 13* −25.224 0.292 1.5346 56.1 (=νd7) 14*2.369 0.140 15 ∞ 0.200 1.5168 64.2 16 ∞ 0.501 (Image ∞ plane) AsphericSurface Data First Surface k = 0.000, A₄ = −1.059E−01, A₆ = 1.519E−01,A₈ = −6.957E−01, A₁₀ = 9.014E−01, A₁₂ = −4.692E−01, A₁₄ = −1.711E−01,A₁₆ = 2.338E−01 Second Surface k = 0.000, A₄ = −2.420E−01, A₆ =3.601E−01, A₈ = −3.128, A₁₀ = 7.058, A₁₂ = −4.769, A₁₄ = −2.705, A₁₆ =3.941 Third Surface k = 0.000, A₄ = −1.054E−01, A₆ = −2.159E−01, A₈ =−6.197E−01, A₁₀ = 1.737, A₁₂ = −5.978E−01, A₁₄ = −5.618E−01, A₁₆ =4.096E−01 Fourth Surface k = 0.000, A₄ = −1.990E−01, A₆ = 1.660E−02, A₈= 5.257E−02, A₁₀ = 5.262E−01, A₁₂ = −7.864E−01, A₁₄ = 7.137E−03, A₁₆ =4.777E−01 Fifth Surface k = 0.000, A₄ = −2.303E−01, A₆ = −5.051E−01, A₈= 1.902, A₁₀ = −2.253, A₁₂ = 7.865E−01, A₁₄ = 7.259E−01, A₁₆ =−4.857E−01 Sixth Surface k = 0.000, A₄ = −1.269E−02, A₆ = −4.889E−01, A₈= 1.274, A₁₀ = −1.695, A₁₂ = 8.861E−01, A₁₄ = 8.995E−02, A₁₆ =−1.334E−01 Seventh Surface k = 0.000, A₄ = 2.686E−01, A₆ = −8.696E−02,A₈ = 1.475E−01, A₁₀ = −4.466E−02, A₁₂ = −4.663E−01, A₁₄ = 4.854E−01, A₁₆= −1.752E−01 Eighth Surface k = 0.000, A₄ = 1.760E−01, A₆ = 7.701E−02,A₈ = 1.205E−01, A₁₀ = −6.102E−02, A₁₂ = −1.408E−02, A₁₄ = −5.581E−03,A₁₆ = 3.934E−03 Ninth Surface k = 0.000, A₄ = −1.778E−01, A₆ =1.010E−01, A₈ = −9.084E−02, A₁₀ = 4.372E−03, A₁₂ = −1.141E−02, A₁₄ =−7.648E−03, A₁₆ = 8.843E−03 Tenth Surface k = 0.000, A₄ = −1.619E−01, A₆= 4.960E−02, A₈ = −2.249E−02, A₁₀ = −9.490E−03, A₁₂ = 2.128E−03, A₁₄ =8.518E−04, A₁₆ = 6.754E−04 Eleventh Surface k = 0.000, A₄ = −2.120E−01,A₆ = 2.271E−03, A₈ = 2.202E−02, A₁₀ = 2.240E−04, A₁₂ = 6.022E−04, A₁₄ =−9.079E−05, A₁₆ = −2.710E−04 Twelfth Surface k = 0.000, A₄ = −1.486E−01,A₆ = 2.966E−02, A₈ = 2.301E−03, A₁₀ = −2.471E−03, A₁₂ = −2.360E−04, A₁₄= 1.248E−04, A₁₆ = 1.563E−05 Thirteenth Surface k = 0.000, A₄ =−1.016E−01, A₆ = 9.787E−02, A₈ = −4.729E−02, A₁₀ = 1.095E−02, A₁₂ =−3.587E−03, A₁₄ = 1.356E−03, A₁₆ = −1.785E−04 Fourteenth Surface k =0.000, A₄ = −2.040E−01, A₆ = 1.305E−01, A₈ = −6.819E−02, A₁₀ =2.475E−02, A₁₂ = −5.881E−03, A₁₄ = 7.921E−04, A₁₆ = −4.569E−05 f1 =14.67 mm f2 = 2.22 mm f3 = −4.63 mm f4 = 7.46 mm f5 = −21.71 mm f6 =−100.33 mm f7 = −4.04 mm f12 = 2.09 mm f45 = 11.40 mm f67 = −3.97 mm

The values of the respective conditional expressions are as follows:f1/f2=6.62f12/f=0.62f2/f3=−0.48f12/f3=−0.45f67/f=−1.18f45/f67=−2.87f7/f6=0.040D34/f=0.098

Accordingly, the imaging lens of Numerical Data Example 4 satisfies theabove-described conditional expressions. The distance on the opticalaxis from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 4.21 mm, anddownsizing of the imaging lens is attained.

FIG. 11 shows a lateral aberration that corresponds to the half angle ofview ω, and FIG. 12 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively, for the imaging lens of NumericalData Example 4. As shown in FIGS. 11 and 12, according to the imaginglens of Numerical Data Example 4, the aberrations are alsosatisfactorily corrected.

NUMERICAL DATA EXAMPLE 5

Basic data are shown below. f = 3.33 mm, Fno = 2.2, ω = 37.0° Unit: mmSurface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 1.998 0.3121.5346 56.1 (=νd1)  2* (Stop) 2.029 0.079  3* 2.212 0.529 1.5346 56.1(=νd2)  4* −3.987 0.031  5* 12.215 0.250 1.6355 24.0 (=νd3)  6* 3.7490.629 (=D34)  7* −2.154 0.407 1.5346 56.1 (=νd4)  8* −1.267 0.039  9*5.866 0.333 1.6355 24.0 (=νd5) 10* 5.255 0.060 11* 3.137 0.298 1.534656.1 (=νd6) 12* 2.173 0.193 13* 11397.590 0.297 1.5346 56.1 (=νd7) 14*2.258 0.200 15 ∞ 0.200 1.5168 64.2 16 ∞ 0.447 (Image ∞ plane) AsphericSurface Data First Surface k = 0.000, A₄ = −1.273E−01, A₆ = 1.508E−01,A₈ = −6.904E−01, A₁₀ = 9.804E−01, A₁₂ = −4.571E−01, A₁₄ = −1.739E−01,A₁₆ = 1.781E−01 Second Surface k = 0.000, A₄ = −2.502E−01, A₆ =3.963E−01, A₈ = −3.044, A₁₀ = 7.055, A₁₂ = −4.876, A₁₄ = −2.735, A₁₆ =4.031 Third Surface k = 0.000, A₄ = −8.921E−02, A₆ = −1.497E−01, A₈ =−6.485E−01, A₁₀ = 1.685, A₁₂ = −5.815E−01, A₁₄ = −4.625E−01, A₁₆ =1.919E−01 Fourth Surface k = 0.000, A₄ = −2.203E−01, A₆ = −1.224E−02, A₈= 3.919E−02, A₁₀ = 5.267E−01, A₁₂ = −7.603E−01, A₁₄ = 4.830E−02, A₁₆ =3.557E−01 Fifth Surface k = 0.000, A₄ = −2.164E−01, A₆ = −5.134E−01, A₈= 1.864, A₁₀ = −2.257, A₁₂ = 7.562E−01, A₁₄ = 7.189E−01, A₁₆ =−4.850E−01 Sixth Surface k = 0.000, A₄ = −2.237E−02, A₆ = −4.625E−01, A₈= 1.272, A₁₀ = −1.689, A₁₂ = 9.042E−01, A₁₄ = 8.765E−02, A₁₆ =−1.767E−01 Seventh Surface k = 0.000, A₄ = 1.892E−01, A₆ = −8.488E−02,A₈ = 1.915E−01, A₁₀ = −6.353E−03, A₁₂ = −4.467E−01, A₁₄ = 4.821E−01, A₁₆= −1.720E−01 Eighth Surface k = 0.000, A₄ = 1.858E−01, A₆ = 5.304E−02,A₈ = 1.167E−01, A₁₀ = −6.230E−02, A₁₂ = −1.436E−02, A₁₄ = −1.115E−03,A₁₆ = 5.918E−03 Ninth Surface k = 0.000, A₄ = −1.667E−01, A₆ =1.096E−01, A₈ = −8.725E−02, A₁₀ = 1.457E−02, A₁₂ = −4.883E−03, A₁₄ =−7.030E−03, A₁₆ = 4.503E−03 Tenth Surface k = 0.000, A₄ = −1.637E−01, A₆= 6.542E−02, A₈ = −2.581E−02, A₁₀ = −1.078E−02, A₁₂ = 2.408E−03, A₁₄ =1.127E−03, A₁₆ = 4.300E−04 Eleventh Surface k = 0.000, A₄ = −2.019E−01,A₆ = −3.117E−03, A₈ = 2.040E−02, A₁₀ = −7.931E−05, A₁₂ = 4.201E−04, A₁₄= −7.934E−05, A₁₆ = −1.698E−04 Twelfth Surface k = 0.000, A₄ =−1.885E−01, A₆ = 3.279E−02, A₈ = 1.241E−03, A₁₀ = −2.764E−03, A₁₂ =−2.670E−04, A₁₄ = 1.320E−04, A₁₆ = 2.895E−05 Thirteenth Surface k =0.000, A₄ = −1.080E−01, A₆ = 9.773E−02, A₈ = −4.668E−02, A₁₀ =1.088E−02, A₁₂ = −3.651E−03, A₁₄ = 1.346E−03, A₁₆ = −1.710E−04Fourteenth Surface k = 0.000, A₄ = −2.023E−01, A₆ = 1.308E−01, A₈ =−6.847E−02, A₁₀ = 2.473E−02, A₁₂ = −5.880E−03, A₁₄ = 7.920E−04, A₁₆ =−4.567E−05 f1 = 54.33 mm f2 = 2.74 mm f3 = −8.61 mm f4 = 4.96 mm f5 =−100.82 mm f6 = −14.82 mm f7 = −4.23 mm f12 = 2.76 mm f45 = 5.10 mm f67= −3.31 mm

The values of the respective conditional expressions are as follows:f1/f2=19.81f12/f=0.83f2/f3=−0.32f12/f3=−0.32f67/f=−0.99f45/f67=−1.54f7/f6=0.29D34/f=0.19

Accordingly, the imaging lens of Numerical Data Example 5 satisfies theabove-described conditional expressions. The distance on the opticalaxis from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 4.24 mm, anddownsizing of the imaging lens is attained.

FIG. 14 shows a lateral aberration that corresponds to the half angle ofview ω, and FIG. 15 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively, for the imaging lens of NumericalData Example 5. As shown in FIGS. 14 and 15, according to the imaginglens of Numerical Data Example 5, the aberrations are alsosatisfactorily corrected.

NUMERICAL DATA EXAMPLE 6

Basic data are shown below. f = 3.37 mm, Fno = 2.2, ω = 37.0° Unit: mmSurface Data Surface Number i r d nd νd (Object) ∞ ∞  1* 1.754 0.3431.5346 56.1 (=νd1)  2* (Stop) 1.779 0.096  3* 2.057 0.500 1.5346 56.1(=νd2)  4* −5.203 0.030  5* 8.410 0.250 1.6355 24.0 (=νd3)  6* 3.2000.403 (=D34)  7* −1.580 0.346 1.5346 56.1 (=νd4)  8* −1.643 0.047  9*−10.498 0.470 1.5346 56.1 (=νd5) 10* −1.513 0.060 11* 5.245 0.342 1.635524.0 (=νd6) 12* 4.341 0.168 13* −3.342 0.365 1.5346 56.1 (=νd7) 14*2.330 0.250 15 ∞ 0.200 1.5168 64.2 16 ∞ 0.597 (Image ∞ plane) AsphericSurface Data First Surface k = 0.000, A₄ = −1.251E−01, A₆ = 1.669E−01,A₈ = −6.668E−01, A₁₀ = 9.053E−01, A₁₂ = −5.258E−01, A₁₄ = −1.012E−01,A₁₆ = 1.986E−01 Second Surface k = 0.000, A₄ = −3.204E−01, A₆ =4.458E−01, A₈ = −3.063, A₁₀ = 6.788, A₁₂ = −5.061, A₁₄ = −1.504, A₁₆ =2.998 Third Surface k = 0.000, A₄ = −1.540E−01, A₆ = −1.263E−01, A₈ =−7.686E−01, A₁₀ = 1.771, A₁₂ = −6.823E−01, A₁₄ = −1.560E−01, A₁₆ =−3.715E−02 Fourth Surface k = 0.000, A₄ = −2.584E−01, A₆ = −2.428E−02,A₈ = 1.690E−01, A₁₀ = 3.337E−01, A₁₂ = −7.684E−01, A₁₄ = 3.283E−01, A₁₆= 1.218E−01 Fifth Surface k = 0.000, A₄ = −2.665E−01, A₆ = −4.280E−01,A₈ = 1.683, A₁₀ = −2.114, A₁₂ = 5.449E−01, A₁₄ = 1.011, A₁₆ = −5.988E−01Sixth Surface k = 0.000, A₄ = −2.117E−02, A₆ = −4.541E−01, A₈ = 1.283,A₁₀ = −1.782, A₁₂ = 9.159E−01, A₁₄ = 1.749E−01, A₁₆ = −2.109E−01 SeventhSurface k = 0.000, A₄ = 1.878E−01, A₆ = −2.029E−01, A₈ = 3.026E−01, A₁₀= 4.645E−02, A₁₂ = −5.625E−01, A₁₄ = 3.660E−01, A₁₆ = −2.208E−02 EighthSurface k = 0.000, A₄ = 1.055E−01, A₆ = −1.020E−01, A₈ = 9.764E−02, A₁₀= −3.036E−02, A₁₂ = 1.045E−05, A₁₄ = 6.110E−04, A₁₆ = 7.310E−03 NinthSurface k = 0.000, A₄ = −1.538E−02, A₆ = 9.087E−02, A₈ = −1.159E−01, A₁₀= 4.385E−02, A₁₂ = 4.559E−03, A₁₄ = −6.675E−03, A₁₆ = 2.121E−04 TenthSurface k = 0.000, A₄ = 1.028E−01, A₆ = 5.866E−02, A₈ = 1.504E−02, A₁₀ =−1.355E−02, A₁₂ = −1.586E−03, A₁₄ = 3.238E−04, A₁₆ = 1.121E−04 EleventhSurface k = 0.000, A₄ = −1.681E−01, A₆ = 1.559E−02, A₈ = −2.368E−03, A₁₀= 1.331E−02, A₁₂ = −5.693E−04, A₁₄ = −1.351E−03, A₁₆ = −1.707E−04Twelfth Surface k = 0.000, A₄ = −2.149E−01, A₆ = 5.930E−02, A₈ =1.207E−03, A₁₀ = −3.015E−03, A₁₂ = 2.723E−04, A₁₄ = 1.587E−04, A₁₆ =−3.731E−05 Thirteenth Surface k = 0.000, A₄ = −6.768E−02, A₆ =9.771E−02, A₈ = −3.986E−02, A₁₀ = 1.101E−02, A₁₂ = −3.971E−03, A₁₄ =1.268E−03, A₁₆ = −1.682E−04 Fourteenth Surface k = 0.000, A₄ =−1.604E−01, A₆ = 1.128E−01, A₈ = −6.563E−02, A₁₀ = 2.480E−02, A₁₂ =−5.899E−03, A₁₄ = 7.955E−04, A₁₆ = −4.663E−05 f1 = 40.46 mm f2 = 2.83 mmf3 = −8.28 mm f4 = 84.01 mm f5 = 3.25 mm f6 = −46.45 mm f7 = −2.51 mmf12 = 2.83 mm f45 = 2.93 mm f67 = −2.43 mm

The values of the respective conditional expressions are as follows:f1/f2=14.32f12/f=0.84f2/f3=−0.34f12/f3=−0.34f67/f=−0.72f45/f67=−1.21f7/f6=0.054D34/f=0.12

Accordingly, the imaging lens of Numerical Data Example 6 satisfies theabove-described conditional expressions. The distance on the opticalaxis from the object-side surface of the first lens L1 to the imageplane IM (air conversion length for the filter 10) is 4.40 mm, anddownsizing of the imaging lens is attained.

FIG. 17 shows a lateral aberration that corresponds to the half angle ofview ω, and FIG. 18 shows a spherical aberration (mm), astigmatism (mm),and a distortion (%), respectively, for the imaging lens of NumericalData Example 6. As shown in FIGS. 17 and 18, according to the imaginglens of Numerical Data Example 6, the aberrations are alsosatisfactorily corrected.

According to the above-described imaging lens of the embodiment, it isachievable to take an image of wide view of angle (2ω), which is as wideas 70° or greater. According to Numerical Data Examples 1 to 6, theimaging lenses have wide angles of view of 74.0°. According to theimaging lens of the embodiment, it is possible to take an image of awider range than that can be taken by a conventional imaging lens.

Moreover, in these years, with advancement in digital zoom technology,which enables to enlarge any area of an image obtained through animaging lens by image processing, an imaging element having a high pixelcount is often used in combination with a high-resolution imaging lens.In case of such an imaging element with a high pixel count, alight-receiving area of each pixel decreases, so that an image tends tobe dark. As a method of correcting the darkness of the image, there is amethod of improving light-receiving sensitivity of the imaging elementby using an electrical circuit. However, when the light-receivingsensitivity increases, a noise component, which does not directlycontribute to formation of an image, is also amplified. Therefore, it isnecessary to have another circuit to reduce the noise. According to theimaging lenses of Numerical Data Examples 1 to 6, the Fnos of theimaging lens are as small as 2.2 to 2.3. According to the imaging lensof the embodiment, it is achievable to obtain a sufficiently brightimage without providing the above-described electrical circuit.

Accordingly, when the imaging lens of the embodiment is mounted in animaging optical system, such as cameras built in portable devicesincluding cellular phones, portable information terminals, andsmartphones, digital still cameras, security cameras, onboard cameras,and network cameras, it is possible to attain both high performance anddownsizing of the cameras.

Accordingly, the present invention may be applicable in an imaging lensto be mounted in relatively small-sized cameras such as cameras that arebuilt in portable devices including cellular phones, smartphones, andportable information terminals, digital still cameras, security cameras,onboard cameras, and network cameras.

The disclosure of Japanese Patent Application No. 2014-083530, filed onApr. 15, 2014, is incorporated in the application by reference.

While the present invention has been explained with reference to thespecific embodiment of the present invention, the explanation isillustrative and the present invention is limited only by the appendedclaims.

What is claimed is:
 1. An imaging lens comprising: a first lens group; asecond lens group having positive refractive power; and a third lensgroup, arranged in this order from an object side to an image planeside, wherein said first lens group includes a first lens havingpositive refractive power, a second lens, and a third lens, said secondlens group includes a fourth lens and a fifth lens, said third lensgroup includes a sixth lens having negative refractive power and aseventh lens having negative refractive power, said first lens is formedin a shape so that a surface thereof on the object side has a positivecurvature radius, said second lens is formed in a shape so that asurface thereof on the object side has a positive curvature radius, saidfifth lens is formed in a shape so that a surface thereof on the objectside has a negative curvature radius, said seventh lens is formed in ashape so that a surface thereof on the object side has a negativecurvature radius, and said seventh lens has an Abbe's number νd7 so thatthe following conditional expression is satisfied:40<νd7<75.
 2. The imaging lens according to claim 1, wherein said firstlens has an Abbe's number νd1, said second lens has an Abbe's numberνd2, and said third lens has an Abbe's number νd3 so that the followingconditional expressions are satisfied:40<νd1<75,40<νd2<75,20<νd3<35.
 3. The imaging lens according to claim 1, wherein said firstlens has a focal length f1 and said second lens has a focal length f2 sothat the following conditional expression is satisfied:2.5<f1/f2<30.
 4. The imaging lens according to claim 1, wherein saidfirst lens and said second lens have a composite focal length f12 sothat the following conditional expression is satisfied:0.5<f12/f<1.1, where f is a focal length of a whole lens system.
 5. Theimaging lens according to claim 1, wherein said second lens has a focallength f2 and said third lens has a focal length f3 so that thefollowing conditional expression is satisfied:−1.0<f2 /f3<−0.2.
 6. The imaging lens according to claim 1, wherein saidfirst lens and said second lens have a composite focal length f12 andsaid third lens has a focal length f3 so that the following conditionalexpression is satisfied:−1.0<f12/f3<−0.1.
 7. The imaging lens according to claim 1, wherein saidsixth lens and said seventh lens have a composite focal length f67 sothat the following conditional expression is satisfied:−1.5<f67/f<−0.5, where f is a focal length of a whole lens system. 8.The imaging lens according to claim 1, wherein said fourth lens and saidfifth lens have a composite focal length f45 and said sixth lens andsaid seventh lens have a composite focal length f67 so that thefollowing conditional expression is satisfied:−3<f45/f67<−0.8.
 9. The imaging lens according to claim 1, wherein saidsixth lens has a focal length f6 and said seventh lens has a focallength f7 so that the following conditional expression is satisfied:0.02<f7/f6<0.3.
 10. The imaging lens according to claim 1, wherein saidthird lens is arranged to be away from the fourth lens by a distance D34on an optical axis thereof so that the following conditional expressionis satisfied:0.03<D34/f<0.2 where f is a focal length of a whole lens system.
 11. Animaging lens comprising: a first lens group; a second lens group; and athird lens group, arranged in this order from an object side to an imageplane side, wherein said first lens group includes a first lens havingpositive refractive power, a second lens, and a third lens, arrangedrespectively with a space in between, said second lens group includes afourth lens and a fifth lens having positive refractive power, arrangedrespectively with a space in between, said third lens group includes asixth lens having negative refractive power and a seventh lens havingnegative refractive power, arranged respectively with a space inbetween, said second lens is formed in a shape so that a surface thereofon the object side has a positive curvature radius, said third lens isformed in a shape so that a surface thereof on the image plane side hasa positive curvature radius, said sixth lens is formed in a shape sothat a surface thereof on the image plane side has a positive curvatureradius, and said seventh lens has an Abbe's number νd7 so that thefollowing conditional expression is satisfied:40<νd7<75.
 12. The imaging lens according to claim 11, wherein saidfirst lens has an Abbe's number νd1, said second lens has an Abbe'snumber νd2, and said third lens has an Abbe's number νd3 so that thefollowing conditional expressions are satisfied:40<νd1<75,40<νd2<75,20<νd3<35.
 13. The imaging lens according to claim 11, wherein saidfirst lens has a focal length f1 and said second lens has a focal lengthf2 so that the following conditional expression is satisfied:2.5<f1 /f2<30.
 14. The imaging lens according to claim 11, wherein saidfirst lens and said second lens have a composite focal length f12 sothat the following conditional expression is satisfied:0.5<f12/f<1.1, where f is a focal length of a whole lens system.
 15. Theimaging lens according to claim 11, wherein said second lens has a focallength f2 and said third lens has a focal length f3 so that thefollowing conditional expression is satisfied:−1.0<f2/f3<−0.2.
 16. The imaging lens according to claim 11, whereinsaid first lens and said second lens have a composite focal length f12and said third lens has a focal length f3 so that the followingconditional expression is satisfied:−1.0<f12/f3<−0.1.
 17. The imaging lens according to claim 11, whereinsaid sixth lens and said seventh lens have a composite focal length f67so that the following conditional expression is satisfied:−1.5<f67/f<−0.5, where f is a focal length of a whole lens system. 18.The imaging lens according to claim 11, wherein said fourth lens andsaid fifth lens have a composite focal length f45 and said sixth lensand said seventh lens have a composite focal length f67 so that thefollowing conditional expression is satisfied:−3<f45/f67<−0.8.
 19. The imaging lens according to claim 11, whereinsaid sixth lens has a focal length f6 and said seventh lens has a focallength f7 so that the following conditional expression is satisfied:0.02<f7/f6<0.3.
 20. The imaging lens according to claim 11, wherein saidthird lens is arranged to be away from the fourth lens by a distance D34on an optical axis thereof so that the following conditional expressionis satisfied:0.03<D34/f<0.2 where f is a focal length of a whole lens system.